import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<ToNumber<'0'>, 0>>,
  Expect<Equal<ToNumber<'5'>, 5>>,
  Expect<Equal<ToNumber<'12'>, 12>>,
  Expect<Equal<ToNumber<'27'>, 27>>,
  Expect<Equal<ToNumber<'18@7_$%'>, never>>,
]

type Digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';

type IsNumber<
  S extends string,
> =
S extends `${Digit}${infer Tail}`
  ? IsNumber<Tail>
  : S extends ''
    ? true
    : false
;

type ToNumber<
  S extends string,
  Acc extends 1[] = []
> =
IsNumber<S> extends true
  ? `${Acc['length']}` extends S
    ? Acc['length']
    : ToNumber<S, [...Acc, 1]>
  : never